The present invention relates to a magnetic tape tracking control apparatus and method, a magnetic tape format, a recording medium and a program. More particularly, the present invention relates to a magnetic tape tracking control apparatus and method, a magnetic tape format, a recording medium and a program for securely capturing data at variable-speed reproduction to display good images.
Recently, the technologies for recording image and audio data after compressing have been making considerable progress. Highly efficient compressing algorithms include the MPEG (Moving Picture Experts Group) standard for example.
For example, in conventional recording devices, such as VTR (Video Tape Recorder), which record image and audio data onto a magnetic tape by use of the MPEG standard, in order to enable variable-speed reproduction (or so-called search reproduction) at other than normal reproduction speeds, search image data is recorded at a position which allows the rotary head to trace at the time of search reproduction.
When search reproduction is executed at a predetermine speed, the search image data is read from the magnetic tape and a search image is displayed on the screen.
In implementing the search capability of recording and reproducing devices, it is desirable to set the value of the high-speed reproduction speed to 24 (a speed at which images are displayed every 2 seconds of normal reproduction speed) in view of the number of update frames (namely, the number of search frames or an image interval) and the quick view time of one roll of magnetic tape.
In the case of 24-fold reproduction, reproduction is executed every 3 ECCs (Error Correcting Codes) (every 48 tracks because 1 ECC block consists of 16 tracks), thereby requiring an optimum tracking system.
In order to implement reliable phase locking, it is desirable to record recording phase information (namely, the value a modulo-3 counter in a unit of ECC or the value of a modulo-48 counter in unit of track) to every sync block. However, this presents a problem that the bit allocation is restricted and, therefore, an increase in the bits of ID, for example, lowers the total efficiency.
It may be possible to record search data repeatedly and lock the phase to one of patterns (in unit of ECC). However, this presents a problem of increasing the volume of the search data 3 times, thereby squeezing the rate of the main video to affect picture quality adversely .
Also, a scheme has been proposed in which tracking information is recorded in the control track formed along the length of magnetic tape. However, this presents the problem of increased cost, thereby making it impracticable for consumer-use DV (Digital Video) formats.